1. Field of Invention
The present invention relates to an apparatus and a method for measuring the amount of gas. The present invention also relates to a standardization means for such a gas measuring device. Typically, these gases are the exhaust gases, emitted through stacks, produced as a result of combustion.
2. Prior Art
Gas measuring apparatus for monitoring the output of combustion at the stack is well known, see for example U.S. Pat. No. 4,076,425. Typically, these devices operate in harsh environments and in locations that are not easily accessible. Some of the problems, caused thereby, are: lamp aging, drift in electronics and dirt build-up on the window. Thus, to operate effectively, i.e. maintain accuracy and repeatability, these devices must have self-contained standardization means.
Heretofore, one standardization means is described in U.S. Pat. No. 3,836,237. That reference teaches, inter alia, the use of air curtains to keep windows clean. However, despite this practice of air curtains, dirt does build up on the window and must be accounted for in the standardization process. U.S. Pat. Nos. 3,838,925 and 4,076,425 teach the use of alternative optical paths to correct for lamp aging and drift in electronics. These references, however, do not teach the correction of other factors, such as dirt on the windows.